(i) For the reaction: PbO2+Pb→2PbO,ΔG°<0 i.e. (−)ve means PbO(Pb2+) is more stable hence it has more characteristic oxidation state. (ii) For the reaction: SnO2+Sn→2SnO,ΔG°>0 i.e. (+) ve, means SnO2(Sn4+) is more stable than Sn2+ (SnO) hence is more characteristic oxidation state. Therefore, characteristic oxidation states for lead and tin are respectively +2 and +4.